As a preventative measure against deterioration of a predetermined area caused by gases containing oxygen, water vapor and the like, materials with gas barrier properties are used in a wide variety of fields including organic light-emitting devices, organic semiconductors, organic solar cells, and thin-film batteries.
The water vapor permeability of such materials is measured using the humidity sensor method or infrared sensor method specified by JIS K-7129, or the calcium corrosion method disclosed in Patent Documents 1 and 2.
Meanwhile, in recent years in the field of organic light-emitting devices, there has been a demand for materials with very high gas barrier properties. The evaluation of such materials requires measurement of water vapor permeability at the level as high as 10−5 g/m2/day.
However, the measurement limit of water vapor permeability is only about 10−3 g/m2/day in the foregoing humidity sensor method, the infrared sensor method, and the calcium corrosion method, and these methods fail to measure water vapor permeability at the level of 10−5 g/m2/day. Another problem is that the measurement of water vapor permeability takes several days even at the level of about 10−3 g/m2/day.    Patent Document 1: JP-A-2005-283561    Patent Document 2: JP-A-2006-250816